"There is an obvious danger of electrocution ... there's also problems with backlash from the cutting of the wire, that could cause serious injury to the body or the head of the person doing it. There's also the risk of being hit by trains while they're taking the wire.''

Police said organised gangs had moved into the scrap-metal business to cash in on soaring world demand for copper and scrap metal, which has doubled in price in the past year.

Connex communications manager Andrew Cassidy said the company had recorded 20 incidents of cable theft since September, which had delayed more than 520 trains.

"Before September it was far less frequent ... it's really only been over the last two or three months that the number has gone up,'' he said.

Mr Cassidy said the company was working with police, but there was little else it could do to tackle the problem.

"There's not a lot we can do ... it's hard to maintain security on 300 kilometres of train track,'' he said.

Copper piping, taps and electrical wiring has been ripped from building sites and schools and up to two tonnes of copper at a time stolen from scrapyards in Melbourne.

The metal industry has been asked to be on the lookout for stolen copper.